Manufacturing method of ceramic slurry, green sheet and multilayer ceramic device

ABSTRACT

A manufacturing method of ceramic slurry being used for producing a green sheet which can have a smooth surface, exhibits a satisfactory sheet strength, and is excellent in workability such as releasing, a green sheet produced by the use of the slurry produced by the method, and a multilayer ceramic device produced by the use of the green sheet is provided. According to the present invention, a manufacturing method of ceramic slurry at least comprising a ceramic powder and a binder resin solution, wherein a high-pressure dispersing treatment of the ceramic powder and a lacquer for preliminary addition, which is a part of the binder resin solution, is carried out so that a shearing rate is set to 1×10 7  to 1×10 8  [1/sec] to prepare a preliminary slurry, and at least a lacquer for post-addition, which a high-pressure dispersing treatment is not applied, is added to the preliminary slurry which a high-pressure dispersing treatment is applied.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of ceramicslurry, more particularly, a manufacturing method of ceramic slurrybeing used for producing a green sheet which can have a smooth surface,exhibits a satisfactory sheet strength, and is excellent in workabilitysuch as releasing, a green sheet produced by the use of a slurryproduced by the method, and a multilayer ceramic device produced by theuse of the green sheet.

2. Description of the Related Art

Developments of ceramic green sheet are performed to obtain ahigh-capacitance multilayer ceramic chip capacitor as an example ofmultilayer ceramic device. The multilayer ceramic chip capacitor has astructure of alternately laminating electrode layers, which one end isexposed to the edge of the chip, and dielectric layers, and both sidesof the laminating direction are covered with the dielectric layers likea lid.

While more dielectric layers in 1 chip can provide a higher capacity,the chip size is fixed. Therefore, in order to make capacitance of thechip large or maintain the capacitance while miniaturizing the chip, thedielectric layer is required to be thin. The dielectric layer isobtained by covering dielectric particles having a diameter of submicron order with resin, i.e. binder, to form a sheet, laminating thesesheets, and firing. Therefore, in order to laminate said dielectriclayers, it becomes important to produce a thin green sheet.

However, when the sheet becomes thin, unevenness on the sheet surfacecannot be ignored. That is, when the sheet is thin, a surface statechange, which was not needed to take into consideration when the sheetwas thick, turns into change of the sheet thickness itself. It isexpected that concaves of the unevenness on the surface becomes weak tovoltage impression after firing, and causes short circuit. Therefore, itis indispensable requirements for manufacturing multilayer chipcapacitor to provide a sheet having a smooth surface, i.e. small changeof a surface roughness, and a uniform thickness.

As factors, which influence the surface unevenness of a sheet, aparticle size of pigments, a paste composition, a dispersing conditionwhen manufacturing the paste, a spreading condition when forming asheet, and a smoothing treatment to the sheet itself, etc. arementioned. The present invention relates to an improvement approach ofthe distributed condition when manufacturing the paste. Pigments notcausing aggregation within the paste and disperse as a single particleform raises surface characteristic and density of the sheet formed withsaid pigments. With the present invention, pigments can be dispersed,and sheet having superior surface characteristic can be manufactured.

In addition, as shown in the following patent reference 1, a method toimprove dispersiveness by performing a high-pressure treatmentparticularly to the binder while manufacturing the paste is proposed.However, with the technique shown in this patent reference 1, since ahigh-pressure dispersion treatment is applied to the paste includingbinder. i.e. resin, as shown in FIG. 2(B), shearing stress is given tonot only pigments but also resin. For this reason, the resin will bedestroyed by the shearing stress, and deterioration in sheet strengthmay be caused.

Patent Reference 1: U.S. Pat. No. 3,387,455

SUMMARY OF THE INVENTION

An Object to Solve The Invention

In view of the above circumstance, an object of the present invention isto provide a manufacturing method of ceramic slurry being used forproducing a green sheet having a smooth surface, exhibits a satisfactorysheet strength, and is excellent in workability such as releasing, agreen sheet produced by the use of a slurry manufactured by the method,and a multilayer ceramic device manufactured by the use of the greensheet.

Means to Solve the Invention

In order to solve the above-mentioned object, the manufacturing methodof ceramic slurry according to the invention is

-   -   a manufacturing method of ceramic slurry according to the        invention at least comprising ceramic powder and binder resin        solution,    -   wherein a high-pressure dispersing treatment of said ceramic        powder and said lacquer for preliminary addition, which is a        part of said binder resin solution, is carried out so that a        shearing rate may be set to 1×10⁷ to 1×10⁸ [1/sec], and a        preliminary slurry is prepared, and    -   at least said lacquer for post-addition, which a high-pressure        dispersing treatment is not applied is added to the preliminary        slurry which a high-pressure dispersing treatment is applied.

By applying a high-pressure dispersing treatment to the slurry, shearingstress is added to the aggregated powders within the slurry. This stressloosens the aggregation and pigments (ceramic powders) may be dispersedto one powdery unit. Since this stress is applied by using only slurry,and no media such as beads is used, contamination does not occur.

Moreover, if resin is mixed in slurry, the shearing force by thepressure is also applied to resin, and the structure of said resin willbe destroyed and molecular weight of the same will be decreased. Thismay cause deterioration in formed sheet strength and a trouble that thedetachability and the conveyance of the sheet get worse. Particularly,it becomes a problem when a thickness of the green sheet is 5 μm orless, particularly 3 μm or less. To the contrary, in the presentinvention, the resin is added in the paste after performing thehigh-pressure treatment so that the shearing stress is not applied tothe resin and the sheet strength is prevented from deterioration evenwhen the sheet is made thinner.

Furthermore, temperature of the paste generally rises when a highpressure dispersing treatment is applied. Therefore, if said highpressure dispersing treatment is excessively applied to a pastecontaining an organic solvent, risk such as explosion, will arise. Tothe contrary, since there is only a small amount of resin and lacquerdissolving the resin, in the treating slurry of the present invention,the pigment ratio as in the treating slurry becomes high, a specificheat of said slurry becomes high, and a temperature rise is suppressed.Therefore, treating the slurry of the present invention is more securecompared to treating the slurry containing whole lacquer. Further,higher pressure treatment can be applied to said slurry of the inventioncompared to the slurry containing whole lacquer, and a smoother sheetcan be obtained by the slurry of the invention.

In this way, a green sheet having a smooth front surface, a gooddispersion of pigments, wherein strength of the sheet does notdeteriorate can be obtained. Further, surface roughness of the sheetbecomes very small with respect to the thickness between layers,therefore, said thickness between layers can be made small and thelayers can be made thinner. With the invention, more numbers of layerscan be laminated as in multilayer ceramic devices such as a multilayerceramic capacitor, and said devices can be more small-sized.

Preferably, an amount of the binder resin contained in theabove-mentioned lacquer for preliminary addition is less than 20 wt %,preferably less than 10 wt %, and 1 wt % or more, preferably, 4 wt % ormore with respect to the whole amount of the resin contained in theceramic slurry finally obtained.

When an amount of binder resin contained in the lacquer for preliminaryaddition is excessively large, there will be little effect of theinvention mentioned above, and when too small, the stability of thedistribution deteriorates causing inclination for a smoothness on thefront surface of the sheet to decline.

In the present invention, preferably, a binder resin of the binder resinsolution is polyvinyl butyral resin or polyvinyl acetal resin. Anddegree of polymerization as in said resin is preferably at least 1000and at most 2600, more preferably, at least 1400 and at most 2600.

In the present invention, when applying a high pressure dispersingtreatment, shearing stress is applied to the preliminary slurry so thatthe shearing rate is set to 1×10⁷ to 1×10⁸ [1/sec], preferably, 2×10⁷ to1×10⁸ [1/sec], more preferably, 3×10⁷ to 1×10⁸ [1/sec].

In the invention, a method for impressing a high pressure tothe-preliminary slurry is not particularly limited, however, a method topour a paste from a nozzle having a small diameter at high speed, amethod of narrowing the path which a paste is poured, are exemplified.

Particularly, when applying a high-pressure treatment using an equipmentwhich applies shearing stress to the preliminary slurry by pouring theslurry into a nozzle having a narrow diameter and impressing with a highpressure, it is desirable that the shearing rate applied to the slurryimpressed by the high-pressure is within the above-mentioned range.

When the shearing rate is too small, dispersion inclines to beinsufficient, when too large, slurry viscosity tends to becomeexcessively low causing an inclination not able to easily form athin-layer sheet having a constant thickness by a method of applying.

In the invention, a particle size of the ceramic powder is preferably0.01 μm to 0.5 μm. Further, in the invention, some of dispersants and/orplasticizers may be added to the preliminary slurry before applying thehigh pressure dispersing treatment, and some of dispersants and/orplasticizers may be added to the preliminary slurry after applying thehigh pressure dispersing treatment.

Green sheet as in the present invention is manufactured by using ceramicslurry obtained by any one of the manufacturing methods mentioned above.Multilayer ceramic device as in the invention is manufactured by usingthe green sheet mentioned above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a multilayer ceramic capacitor accordingto an embodiment of the present invention.

FIG. 2A is a flow chart showing a manufacturing method of ceramic slurryaccording to an embodiment of the present invention.

FIG. 2B is a flow chart showing a manufacturing method of ceramic slurryaccording to conventional method.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, the invention is described based on the embodiments shown inthe drawings of the invention.

The whole composition of multilayer ceramic capacitor is described as anembodiment of multilayer ceramic device manufactured by the ceramicslurry and the green sheet according to the invention.

As shown in FIG. 1, a multilayer ceramic capacitor 2 according to anembodiment of the present invention comprises capacitor element body 4,the first external electrode 6, and the second external electrode 8. Thecapacitor element body 4 comprises dielectric layers 10 and internalelectrode layers 12, wherein dielectric layers 10 and internal electrodelayers 12 are alternately laminated. One side of the alternatelylaminated internal electrode layers 12 are electrically connected toinside of the first external electrode 6 which is formed at one endportion of the capacitor element body 4. Further, the other side of thealternately laminated internal electrode layers 12 are electricallyconnected to inside of the second external terminal electrode 8 which isformed at the other end portion of the capacitor element body 4.

Material of the dielectric layer 10 is not particularly limited, andcomprises dielectric materials such as barium calcium, strontiumtitanate and/or barium titanate. The thickness of each dielectric layer10 is not particularly limited, but generally it is several μm toseveral hundreds of μm. Particularly in the present embodiment, it ispreferably made thinner to 5 μm or less, more preferably, 3 μm or less.

Material of the terminal electrodes 6 and 8 are not particularlylimited, but normally, copper, copper alloys, nickel, nickel alloys,etc. is used. Further, silver and an alloy of silver and palladium canalso be used. The thickness of terminal electrodes 6 and 8 are also notparticularly limited, but normally around 10 to 50 μm.

Configuration and size of the multilayer ceramic capacitor 2 cansuitably be determined by its purpose of use. When the multilayerceramic capacitor 2 is a rectangular parallelepiped configuration, itsextent is generally the following: length of 0.6 to 5.6 mm, preferably,0.6 to 3.2 mm×width of 0.3 to 5.0 mm, preferably, 0.3 to 1.6 mm×athickness of 0.1 to 1.9 mm, preferably, 0.3 to 1.6 mm.

Next, an example of manufacturing method of multilayer ceramic capacitor2 according to an embodiment of the invention is explained below.

First, in order to manufacture ceramic green sheet which will composedielectric layer 10 shown in FIG. 1 after firing, a paste for greensheet, (ceramic slurry) is prepared.

In the present embodiment, ceramic slurry as a paste for green sheet ismanufactured by a flow chart shown in FIG. 2(A). First, a pigment(ceramic powder) is prepared.

The pigment comprises a main component powder (dielectric particles)such as calcium titanate, strontium titanate and/or barium titanate,which become a main component of the green sheet, and additionalparticles (additional powder) added with said dielectric particles.

Particle size of the main component powder is generally larger than thatof the additional powder, and is around 0.01 or more and 0.5 μm or less,preferably 0.4 μm or less. In addition, in order to form an extremelythin green sheet, it is desirable to use particles finer than thethickness of the green sheet.

The additional powder includes at least one from alkaline-earth metal,transition metal, rare-earth element or glass composition. Saidalkaline-earth metal, transition metal, rare-earth element are used notonly in the state of single element powder, but those oxides, compositeoxides, and the various compounds to be the oxides, such as carbonate,nitrate, hydroxide, organometallic compound those in the powdery formmay be included in the additional powder. Such additional powders aregenerally contained in the paste for green sheet at a small amount ofaround 3 to 6 parts by weight with respect to 100 parts by weight ofmain component powder. Note that as an additional powder, a powderobtained by previously mixing an additional component by ball mill,dried, preliminary fired at 800 to 1000° C., and coarsely pulverized canbe used.

According to the present embodiment, the high pressure dispersingtreatment is applied to the pigment together with solvent and a part oflacquer (a binder resin solution). Said solvent is not particularlylimited, but glycols, alcohol, ketones, esters and/or aromatic solventare exemplified.

Ethyl carbitol, butanediol, 2-butoxyethanol, etc. are exemplified asglycols. Methanol, ethanol, propanol, butanol, etc. are exemplified asalcohol. Acetone, methyl ethyl ketone (MEK), diacetone alcohol, etc. areexemplified as ketones. Further, methyl acetate, ethyl acetate, etc. areexemplified as esters.

Toluene, xylene, benzyl acetate, etc. are exemplified as aromaticsolvent.

Lacquer (resin solution) is a resin dissolved in an organic solution.Said resin is not particularly limited, but acrylic resin, polyvinylbutyral resin, polyvinyl acetal resin, ethyl cellulose resin may beused, however, polyvinyl butyral resin and polyvinyl acetal resin areused in the present embodiment in order to make the layer of the sheetthinner. Degree of polymerization of polyvinyl butyral resin andpolyvinyl acetal resin is 1000 or more and 2600 or less, preferably 1400or more and 2600 or less. Further, butyralization degree in the resin ismore than 64% and less than 78%, preferably more than 64% and less than70%, and an amount of residual acetyl group is less than 6%, preferably3% or less.

Degree of polymerization of polyvinyl butyral resin or polyvinyl acetalresin can be measured by such as that of polyvinyl alcohol resin whichis a raw material of those. Further, butyralization degree in the resincan be measured based on JISK6728. Furthermore, an amount of residualacetyl group can be measured based on JISK6728.

When degree of polymerization of polyvinyl butyral resin is too small,there is an inclination that the layers, which is preferably madethinner to 5 μm or less, more preferably 3 μm or less, may not provide asufficient mechanical strength. While too large, it is in theinclination for the surface roughness to deteriorate when it is formedto a sheet. Further, when butyralization degree in polyvinyl butyralresin is too small, solubility into the paste tends to deteriorate,while when too large, it is in the inclination for the sheet surfaceroughness to deteriorate. Furthermore, when an amount of residual acetylgroup is too large, the sheet surface roughness tends to deteriorate.

Organic solvent used for the lacquer is not particularly limited, butalcohol, butyl carbitol, acetone, toluene, etc. can be used. In thepresent embodiment, the organic solvent preferably comprises an alcoholsolvent and an aromatic solvent, wherein said aromatic solvent is 10parts by weight or more to 20 parts by weight or less when a totalamount of the alcohol solvent and the aromatic solvent is 100 parts byweight. When an amount of the aromatic solvent is too small, the sheetsurface roughness tends to deteriorate, while too large, filtrationcharacteristic of the paste tends to deteriorate, and sheet surfaceroughness tends to increase causing deterioration of the sheet.

Methanol, ethanol, propanol, butanol, etc. are exemplified as alcoholsolvent. Toluene, xylene and benzyl acetate, etc. are exemplified asaromatic solvent.

Binder resin is dissolved and filtered in a alcohol solvent selected atleast one from methanol, ethanol, propanol or butanol, to make asolution, then, main component powder and the other components arepreferably added to the solution. Binder resin having a high degree ofpolymerization is difficult to be dissolved in the solvent, and with ageneral method, dispersion of their paste tends to deteriorate.According to a method of an embodiment of the present invention, binderresin having a high degree of polymerization is first dissolved in theabove-mentioned good solution, and then main component powder and theother components are dissolved in the obtained solution. Accordingly,with the method, paste dispersion can be improved and generation ofnon-dissolved resin can be suppressed. In addition, the solvents otherthan the above-mentioned solvents are unable to raise concentration of asolid content, and a change of lacquer viscosity tends to increase astime passes.

In the present embodiment, when a high pressure dispersing treatment isapplied to pigment, solvent, and a part of lacquer (lacquer forpreliminary addition) as preliminary slurry, a shearing stress isapplied so that the shearing rate is set to 1×10⁷ to 1×10⁸ [1/sec],preferably, 2×10⁷ to 1×10⁸ [1/sec], more preferably, 3×10⁷ to 1×10⁸[1/sec]. When said shearing rate at the high pressure dispersingtreatment is too low, dispersion tends to decrease. The high pressuredispersing treatment may be done by pouring the preliminary slurry intoa nozzle having a small diameter. Further, dispersants and/orplasticizers may be added to the preliminary slurry when applying thehigh pressure dispersing treatment.

The high pressure dispersing treatment is not applied to a remaininglacquer (lacquer for post-addition), and added after the treatment isapplied. Ratio of the lacquer for the preliminary addition and thelacquer for post-addition is, considering a total amount of binder resinincluded in the finally obtained green sheet paste as 100 wt %, binderresin included in the lacquer for preliminary additional is less than 20wt %, preferably less than 10 wt %, and 1 wt % or more, preferably 4 wt% or more.

After high pressure dispersing treatment is applied, together with thelacquer for post-addition, additives selected from dispersants,plasticizers, antistatic agent, dielectric, glass frit, insulators, arekneaded depending on the situation. Said additives may be added afterapplying the high pressure dispersing treatment, but may be added beforeapplying the same and said high pressure dispersing treatment may beapplied to the additives together with the preliminary slurry.

Conditions of kneading after the high pressure dispersing treatment arenot particularly limited, but may be mixed with ball mill.

Dispersants are not particularly limited, but dispersants of maleicacids, polyethylene glycols and/or allylether copolymers areexemplified. Dioctyl phthalate is preferably used as plasticizer,however, it is not particularly limited in the present invention and canbe suitably selected according to the binder resin. Further, antistaticagent is not particularly limited, but preferably imidazoline-basedantistatic agent.

A paste for green sheet (ceramic slurry) manufactured by the flow chartshown in FIG. 2(A) is formed to a sheet state with die coater method tobe a green sheet. These green sheets become dielectric layers 10 asshown in FIG. 1, and are alternately laminated with electrode films,which become internal electrode layers 12, then, cut to be a multilayerchip, and subjected to binder removal processing and firing, to be acapacitor element body 4.

Note that electrode film can be formed with a thick-film forming methodsuch as printing method using electrode paste, or with a combination ofthin-film forming method such as deposit or spattering and a method oftransferring.

Note that binder removal processing may be applied under a generalcondition, however, when using base metals such as Ni or Ni alloys forconductive materials of internal electrodes, the following conditionsmay be particularly preferable.

-   -   heating rate: 5 to 300° C./hour    -   retaining temperature: 200 to 400° C.    -   retaining time: 0.5 to 20 hours    -   gas for ambient atmosphere: wet mixed gas of N₂ and H₂

Firing conditions are preferably the following condition.

-   -   heating rate: 50 to 500° C./hour    -   retaining temperature: 1100 to 1300° C.    -   retaining time: 0.5 to 8 hours    -   cooling rate: 50 to 500° C./hour    -   gas for ambient atmosphere: wet mixed gas of N₂ and H₂

The oxygen partial pressure in the firing atmosphere is preferably 10⁻²Pa or less, more preferably 10⁻² to 10⁻⁸ Pa. When the oxygen partialpressure exceeds the above range, the internal electrode layer tends tobe oxidized, while when excessively lower than the above range,electrode materials in the internal electrode layer is abnormallysintered to be broken in some cases.

Heat treatment after such firing is done by keeping the retainingtemperature or the highest temperature preferably at least 1000° C.,more preferably 1000 to 1100° C. When retention temperature or thehighest temperature during the heat treatment is less than theabove-mentioned range, oxidation of dielectric materials will beinsufficient, and insulation resistance lifetime tends to be shortened,while when more than the above-mentioned range, Ni of inner electrode isnot only oxidized, and the capacitance tends to decrease but react withthe dielectric base and lifetime tends to decrease. Oxygen partialpressure when heating is higher than that of reducing atmosphere whenfiring, and preferably 10⁻³ Pa to 1 Pa, more preferably 10⁻² Pa to 1 Pa.When said oxygen partial pressure when heating is less than theabove-mentioned range, it is difficult to reoxidize the dielectric layer2, while more than the above-mentioned range, internal electrode layer 3tends to oxidize. The other heat treatment conditions are preferably thefollowing.

-   -   Retaining time: 0 to 6 hours    -   cooling rate: 50 to 500° C./hour    -   gas for ambient atmosphere: wet N₂ gas or so

A wetter, etc. may be used to wet the N₂ gas and mixed gas, etc. In thiscase, the water temperature is preferably 0 to 75° C. or so. The binderremoval processing, firing and heat treatment may be performedcontinuously or separately. When performing continuously, it ispreferable that the atmosphere is changed without cooling after thebinder removal processing, the temperature is raised to the retainingtemperature of firing to perform firing, then, cooled to the retainingtemperature of heat treatment and the heat treatment is performed bychanging the atmosphere. On the other hand, when performing separately,at the time of firing, it is preferable that the temperature is raisedto the retaining temperature of the binder removal processing in anatmosphere of a N₂ gas or a wet N₂ gas, the atmosphere is changed, andthe temperature is furthermore raised. And after cooling the temperatureto the holding temperature of the heat treatment, it is preferable thatthe cooling continues by changing the atmosphere again to a N₂ gas or awet N₂ gas. Also, in the heat treatment, after raising the temperatureto the holding temperature under the N₂ gas atmosphere, the atmospheremay be changed, or the entire process of the heat treatment may be in awet N₂ gas atmosphere.

End surface polishing, for example, by barrel polishing or sand blast,etc. is performed on the sintered body (element body 4) obtained asabove, and the external electrode paste is baked to form externalelectrodes 6, 8. A firing condition of the external electrode paste ispreferably, for example, at 600 to 800° C. in a wet mixed gas of N₂ andH₂ for 10 minutes to 1 hour or so. A cover layer is formed by plating,etc. on the surface of the external electrodes 6, 8 if necessary. Noteexternal electrode paste can be prepared in the same way as theabove-mentioned electrode paste.

A multilayer ceramic capacitor of the present invention produced asabove is mounted on a print substrate, etc. by soldering, etc. and usedfor a variety of electronic apparatuses, etc.

In the present embodiment, as shown in FIG. 2(A), shearing stress isapplied to aggregated powders in slurry by applying a high-pressuredispersing treatment to the preliminary slurry. With this method, theaggregated powders are disaggregated and pigments (ceramic powder) aredispersed to one particle per each unit. Since this stress is appliedonly using the slurry and does not require media such as bead,contamination does not occur.

Moreover, when a resin is mixed in the slurry, the shearing stress by apressure is also applied to the resin, causing the destruction of theresin and a decrease of a molecular weight. This will deterioratestrength of the obtained sheet, and also detachability and conveyance ofthe sheet. To the contrary, the binder resin as in the embodiment ispoured in the paste after the high pressure treatment is applied, andthe shearing stress is not applied to the binder resin, therefore,deterioration of the sheet strength is prevented.

Furthermore, temperature of the paste generally rises when high pressuredispersing treatment is applied. Therefore, if said high pressuredispersing treatment is excessively applied to a paste containing anorganic solvent, risk such as explosion, will arise. To the contrary,since there is only a small amount of resin and lacquer dissolving theresin in the treating slurry of the present embodiment, there is anadvantage that the pigment ratio as in the treating slurry becomes high,a specific heat of said slurry becomes high, and a temperature rise issuppressed. Therefore, treating the slurry as in the present inventionis more secure compared to treating slurry containing whole lacquer.Further, higher pressure treatment can be applied to said slurry of theinvention compared to the slurry containing whole lacquer, and asmoother sheet can be obtained by the slurry of the invention.

In this way, a green sheet having a smooth front surface, a gooddispersion of pigments, wherein strength of the sheet does notdeteriorate can be obtained. Further, surface roughness of the sheetbecomes very small with respect to the thickness between layers,therefore, said thickness between layers can be made small and thelayers can be made thinner. With the invention, more numbers of layerscan be laminated as in multilayer ceramic devices such as a multilayerceramic capacitor, and said devices can be more small-sized.

Note that the present invention is not limited to the embodimentdescribed above and can be varied within the scope of the invention.

For instance, ceramic slurry according to the present invention is notlimited to the paste for green sheet as described in the embodimentmentioned above, but can suitable used as the other ceramic slurries,such as electrode past or blank paste.

Further, the multilayer ceramic device manufactured by using the ceramicslurry according to the invention is not limited to multilyaer ceramiccapacitor, but inductor, varistor, etc. are exemplified.

EXAMPLES

Next, the present invention will be explained further in detail bytaking more specific examples of the embodiment of the presentinvention, but the present invention is not limited to the examples.

Example 1 Manufacturing Method of a Paste for a Green Sheet (CeramicSlurry)

BaTiO₃powder (BT-02/Sakai Chemical Industry Co., Ltd.) is used for astarting material of a ceramic powder. With respect to 100 parts byweight of BaTiO₃ powder, 1.48 parts by weight of (Ba_(0.6)Ca_(0.4))SiO₃,1.01 parts by weight of Y₂O₃, 0.72 wt % of MgCO₃, 0.13 wt % of Cr₂O₃,and 0.045 wt % of V₂O₅ are prepared for subcomponent additives of theceramic powder.

First, only the subcomponent additives were mixed by ball mill to makeslurry. Namely, the subcomponent additives (total amount of 8.8 g), 15grams of solvent having a ratio of ethanol:propanol:xylene=42.5:42.5:15,and dispersants (0.1 g) were preliminary pulverized for 20 hours toobtain the subcomponent additives of pulverized slurry.

Next, with respect to BaTiO₃: 191.2 g, 24 g of the subcomponentadditives of pulverized slurry, 123 g of ethanol, 123 g of n-propanol,56 g of xylene, 136 g of diethylene glycol monoethyl ether (DGME), 15 gof mineral spirit, 1.4 g of dispersants, 6 g of DOP (dioctyl phthalate),0.8 g of antistatic agent of imidazolines, and 3.3 g of lacquer ofpolyvinyl butyral resin (lacquer for preliminary addition) are appliedwith a high-pressure dispersing treatment to obtain preliminary slurry.

The high-pressure dispersing treatment is done by using thehigh-pressure dispersing device (ultimaizer HJP-25005 of Sugino MachineCo.) under a condition of 100 MPa. Shearing rate applied to the slurryduring the high-pressure dispersing treatment was calculated from thediameter of a nozzle of the treatment device and treated rate of theslurry and it was 5.10×10⁷ [1/sec] as shown Table 2. The temperature ofthe slurry after applying the high-pressure dispersing treatment was 42°C. as shown in Table 2.

Then, 78.8 g of the same lacquer mentioned above (lacquer forpost-addition) except the high-pressure dispersing treatment was notapplied, was added to the preliminary slurry after the high-pressuredispersing treatment was applied, and kneaded to obtain ceramic slurry(a paste for green sheet). Kneading condition was 16 hours of ball millmixing.

For lacquer, 15% lacquer (BH6 of Sekisui Chemical Co. was dissolved inethanol/n-propanol=1:1) of BH6 of Sekisui Chemical Co. (Polybutyralresin/PVB) was used. Degree of polymerization as in polybutyral resinused as binder resin was 1400, the butyralization degree was 69±3% andresidual acetyl groups were 3±2%. Further, as dispersants, noniondispersants of polyethylene glycol groups (HLB=5 to 6) were used.

When the total wt % of binder resin included in finally obtained pastefor green sheet was 100 wt %, the additional amount of binder resinincluded in lacquer for preliminary addition was 4.2 wt %. The viscosityof finally obtained paste for green sheet was 20 cP. Note that theviscosity of the paste was measured by using B type viscometer and S21as rotor at 25° C. immediately after a drop of the paste came out fromthe mill. Measuring revolution was 50 rpm.

Manufacturing Method of Green Sheet

Paste obtained by the above-mentioned method is applied on the PET filmused as support film by using wire bar coater and dried to obtain greensheet having a thickness of 1 μm. Rate of applying the paste was 50m/min., temperature of furnace for drying was 60 to 70° C., and dryingtime was 2 minutes.

Stability when applying the paste was examined. The results are shown inTable 1. The stability was examined as following. When viscosity of thepaste is 10 cP or less, it becomes difficult to provide a thin layeredsheet having a constant thickness, therefore, when said viscosity wasmore than 10 cP, it was considered good, and the rest was consideredbad.

Evaluation of Green Sheet

Next, glossiness of the green sheet was measured. The glossiness wasmeasured based upon JIS Z-8741 (1983) method 3 by using VGS-LD of JapanDensyoku Industries Co., Ltd. The results are shown in Table 1. Whenmeasuring the glossiness, it was considered to be good when 70% or more,and the rest was considered to be bad. When the glossiness is less than70%, characteristic of the sheet surface becomes inferior and when madeto a chip, it causes short-circuit.

Sheet strength of the green sheet was also measured. 5 sheets punched tobe dumbbell shaped forms were prepared as samples, and each sample wasstretched by a tensile rate of 8 mm/min using a tensile test device ofInstron 5543 and strength of each tension fracture was measured, then,an average value of those was calculated to obtain the sheet strength.The results are shown in Table 1. When the sheet strength is less than4.5 MPa, it will be difficult to release thin-layered sheet having athickness of around 1 μm, and it will provide a great disadvantage tothe manufacturing method. Therefore, as in table 1, when the sheetstrength is 4.5 MPa or more, it is considered to be good and the rest tobe bad. TABLE 1 a ratio of resin an amount of included in lacquer resinwhen applying for preliminary viscosity stability 1 μm a high pressureaddition to a whole of when sheet sheet 1 μm dispersing treatment amountof resin paste applying glossiness glossiness strength sheetComprehensive [PHP] [wt %] [cP] paste [%] determination [MPa] releaseEvaluation Ref. Ex. 1 not applied not applied 21 ◯ 53 x 6.2 ◯ x Ex. 1 0.25 4.2 20 ◯ 73 ◯ 6.2 ◯ ◯ Ex. 2 0.5 8.3 19 ◯ 73 ◯ 6.1 ◯ ◯ Ex. 3 1  16.7  18 ◯ 74 ◯ 5.9 ◯ ◯ Ref. Ex. 2 6   100.0  9 x 76 ◯ 4.1 x x◯: goodx: bad

TABLE 2 an amount of a ratio of resin resin when applying included inlacquer temperature 1 μm a high pressure for preliminary additionsheering of sheet 1 μm dispersing treatment to a whole amount of resinrate paste glossiness strength sheet Comprehensive [PHP ] [wt %] [1/s][° C.] [%] [MPa] release Evaluation Ex. 1 0.25 4.2 5.10E=07 42 73 6.2 ◯◯ Ex. 1-2 0.25 4.2 8.20E+07 63 79 6.1 ◯ ◯ Ref. Ex. 2 6 100 4.50E+07 4976 4.1 x x Ref. Ex. 2-2 6 100 7.20E+07 70 — — — x

Example 2

Green sheet was manufactured in the same way as in Example 1 except anamount of binder resin included in lacquer for preliminary addition was8.3 wt %, with respect to 100 wt %, of a total amount of binder resinincluded in the finally obtained paste for green sheet, and evaluated inthe same way as in Example 1. The results are shown in Table 1.

Example 3

Green sheet was manufactured in the same way as in Example 1 exceptbinder resin included in lacquer for preliminary addition was 16.7 wt %,with respect to 100 wt %, of a total amount of binder resin included inthe finally obtained paste for green sheet. The manufactured green sheetwas evaluated in the same way as in Example 1. The results are shown inTable 1.

Reference Example 1

Green sheet was manufactured in the same way as in Example 1 exceptlacquer for post-addition was not added, a high-pressure dispersingtreatment was not applied, and all the components were mixed for 16hours by a ball mill. The manufactured green sheet was evaluated in thesame way as in Example 1. The results are shown in Table 1 and 2.

Reference Example 2

Green sheet was manufactured in the same way as in Example 1 exceptbinder resin included in lacquer for preliminary addition was 100 wt %(lacquer for post-addition was not added), with respect to 100 wt %, ofa total amount of binder resin included in the finally obtained pastefor green sheet. The manufactured green sheet was evaluated in the sameway as in Example 1. The results are shown in Table 1.

Example 1-2

Green sheet was manufactured in the same way as in Example 1 except thehigh-pressure dispersing treatment was applied under the pressure of 160MPa and shearing rate of 8.20×10⁷ [1/sec]. The manufactured green sheetwas evaluated in the same way as in Example 1. The results are shown inTable 2. Temperature of the paste was 63° C.

Reference Example 2-2

Green sheet was manufactured in the same way as in Example 1 except thehigh-pressure dispersing treatment was applied under the pressure of 160MPa and shearing rate of 7.20×10⁷ [1/sec]. The manufactured green sheetwas evaluated in the same way as in Example 1. The results are shown inTable 2. Here, temperature of the paste became 70° C., which is nearly aboiling point of organic solvent component in the paste and it wasnecessary to take measures to prevent exploding and was not able tomanufacture sheet under usual condition.

Comprehensive Evaluation

Comprehensive evaluation as in Tables 1 and 2 was considered to be badwhen any one of paste stability, glossiness, and sheet release wasconsidered to be bad, and the rest was considered to be good.

From the results shown in Table 1, the comprehensive evaluation wasconfirmed to improve when an amount of binder resin included in lacquerfor preliminary addition was 1 wt % or more and less than 20 wt %, withrespect to whole binder resin included in the finally obtained paste forgreen sheet.

1. A manufacturing method of ceramic slurry at least comprising aceramic powder and a binder resin solution, wherein a high-pressuredispersing treatment of the ceramic powder and a lacquer for preliminaryaddition, which is a part of the binder resin solution, is carried outso that a shearing rate is set to 1×10⁷ to 1×10⁸ [1/sec] to prepare apreliminary slurry, and at least a lacquer for post-addition, which ahigh-pressure dispersing treatment is not applied, is added to thepreliminary slurry which a high-pressure dispersing treatment isapplied.
 2. The manufacturing method of ceramic slurry as set forth inclaim 1, wherein an amount of the binder resin contained the lacquer forpreliminary addition is less than 20 wt % and 1 wt % or more withrespect to the whole amount of resin contained in the finally obtainedceramic slurry.
 3. The manufacturing method of ceramic slurry as setforth in claim 1, wherein, when applying the high pressure dispersingtreatment, shearing stress is applied to the preliminary slurry so thatthe shearing rate is set to 2×10⁷ to 1×10⁸ [1/sec].
 4. The manufacturingmethod of ceramic slurry as set forth in claim 1, wherein a binder resinof the binder resin solution is polyvinyl butyral resin or polyvinylacetal resin.
 5. The manufacturing method of ceramic slurry as set forthin claim 4, wherein degree of polymerization of the binder resin is atleast 1000 and at most
 2600. 6. The manufacturing method of ceramicslurry as set forth in claim 1, wherein the high pressure dispersingtreatment is applied by pouring the preliminary slurry from a wide pathto a narrow path under a high pressure.
 7. The manufacturing method ofceramic slurry as set forth in claim 1, wherein a particle size of theceramic powder is 0.01 μm to 0.5 μm.
 8. The manufacturing method ofceramic slurry as set forth in claim 1, wherein at least a part ofdispersants and/or plasticizers is added to the preliminary slurrybefore applying the high pressure dispersing treatment.
 9. Themanufacturing method of ceramic slurry as set forth in claim 1, whereinat least a part of dispersants and/or plasticizers is added to thepreliminary slurry after applying the high pressure dispersingtreatment.
 10. A green sheet manufactured by using the ceramic slurryobtained by the manufacturing method of ceramic slurry as set forth inclaim
 1. 11. A multilayer ceramic device manufactured by the green sheetas set forth in claim 10.